Method of discharging pulp-digesters.



G. N. WAITE.

METHOD OF DISOHARGING PULP DIGESTERS.

APPLICATION FILED MAY 14, 1908.

Patented Mar. 29, 1910.-

INVENTOR P an n nmnumccmxmmwmruc: 21 vi 4' ATTORNEY. I,

CHARLES N. WAITE, OF WILMINGTON. DELAWARE.

METHOD OF DISCHARGING PULP-DIGESTEBS.

Sp eclfication of Letters Patent.

Patented Mar. 29, 1910.

' Application filed May 14, 1908. Serial No. 432,773.

1'0 all whom it may concern:

Be it known that I, CHARLES N. WArrn, a citizen of the United States of Amerlca,

residing in W'ilmington, in the county of cooked for several hours at such atempera- V lodging against the lower wall of the digester. This is objectionable since thepor-,

ture and under such conditions that a steam pressure of about 120 lbs. is maintained in the digester. When the pulpforming material has been sufiiciently cooked a discharge orificeat the lower end of the digester is opened and the pulp. is discharged into a chamber ordinarily called the blowpit, by the pressure of the steam on the upper end of the digester on the mass of pulp and cooking liquor in the lower end of the digester. The pressure in the blowpit is usually maintained approximately equal to the pressure of the atmosphere and the success of the pulp forming operation depends in part on the disintegration of the pulp which occurs when the pulp enters the blowpit, and is due to the conversion into a steam of the cooking liquor with which the pulp is saturated. This conversion into steam is of course due to the fact that the pressure in "the blowpit is far below the steam pressure corresponding to the temperature of the liquor in the pulp when it enters the blowpit.

Heretofore difliculty has been experienced in the operation of discharging pulp digesters as above described from the fact that all of the pulp does not always pass out of v thexdigester withthe cooking liquor, a portion of the pulp "frequently adhering to or tion remaining prevents the proper amount offresh chips or like pulp forming material from being put into the digester at the followin charging o eration and because the portion of the c arge which is twice cooked is injured by the second cooking operation.

The object of the present invention is the provision of a simple and effective method by which the digester may be thoroughly cleaned and emptied during each dischar e operation without interfering with tie maintenance of the proper steam pressure in the digester to force out the cooking liquor and pulp and to disrupt the latter in the blowpit, and without appreciably diluting the used cooking liquor or otherwise making it more difficult to recover the valuable chemical constituents of such liquor.

In carrying out my invention I provide a tank or like closed receptacle having a valved discharge connection leading from its bottom into the digester and having a steam inlet or supply connection from a suitable steam supply source. This receptacle I partially fill with the black liquor z'. 6., waste liquor from previous pulp cooking operations. I put the liquor in the tank under a steam pressure approximately equal to the working pressure in the digester and heat the liquor to a corresponding pressure. WVhen the digester is to be discharged, and usually after the discharge operation is started, I empty liquor from the tank into the digester. By proceeding in this manner I am able to introduce liquor into the digester to work out of it all the pulp at each discharge operation. As the liquor in the tank is heated to or above the temperaturethen existing in the digester it does not tend to condense the steam in the digester and serves in the blowpit to disrupt the pulp which is carried out with it.

The various features of novelty which characterize my invention are pointed out with articularity in the claims annexed to. and orming a art of this specification. For a better un erstanding of the invention, however, and the advantages possessed by it, reference may be had to the accompanying drawings and descriptive matter in which have illustrated one method by which the invention may be carried out and one form of apparatus which may be used in carrying out the invention.

The drawing is a diagrammatic elevation of a portion of a pulp making plant equipped with my invention.

1 In the plant shown by the drawin there are a series of similar digesters A Q which two are shown. Each of the digesters A opens at its lower end to a common discharge pipe when the corres onding cook or valve B is opened. Each igester may be or strainer E or internally charged at its upper end when the manhole cover A is removed. Pipe C leads to the blowpit or chamber D' open at its upper end through large lpipe to the atmosphere. A pi e D eading from the lower end of the b owpit carried the liquor and pulp to a wash it E, which has a screen liquid discharge pipe E leads from pit E to the black liquor reservoir F. A pump and pipe connections F, G, Gr and G* serve to carry such of the black liquor from reservoir F as is needed either to the upper end of blowpit D to wash down the pulp in it or into the tank H accordingly as valves G and G are set.

The tank H has leading from its lower end a discharge ipe H having in it acock H and connecte to a distribution pi e H 'from which runs branches H contro ed by cocks H to the various digesters A. The tank H. is provided with steam gage H, blow off cock H, safety valve H and water glass H". A steam supply pipe I leads into the tank H and has a perforated portion I extending alongthe bottom of the tank. A valve I controls the admission of steam into the tank H through pipe I from a suitable source of steam supply not shown.

The chips or other pulp forming material is admitted to each digester through the door or manhole formed inits upper end, and normally closed by the cover A'. The cooking liquor is admitted in any suitable manner. The digesters may be heated externally b blowing steam into them. Similarly the lack liquor in the tank E may be heated solely by steam admitted through pipe or bysteam heating coils or in any other suitable manner.

' To fill the tank H the valve I is closed and the .blow oif cock H is opened to permit the steam in the tank to pass out. The valve G5 is then 0 ened andva'lve G is closed. The pump then forces the waste liquor from reservoir F into the tank H. When the tank contains the desired amount of liquor the valves or cocks Gr and H 'are closed. The valve 1 is thenopened and the desired pressure and temperature conditions in the tank H are created. In practice I usually build the pressure in the tank H.

to something less than the cooking pressure in the digester A. If the latter is 120 ounds I make the pressure in the tank Ha out 110 pounds. Y

In discharging a digester A, I firstopen the cock Band wait until the pressure in the digester has fallen somewhat below the pres-' sure in tank H, then I open the appropriate valve H and admit'liquor from tank H into the digester A. A baflie plate A or other spreading device may be located in the digester to cause the liquor to be properly dis-- tributed. The liquor thus-admitted serves to wash out the digester and carry with it into pipe C all the pulp in the digester. On account of its temperature it does not tend to condense the steam in the digester, but on the contrary assists in maintaming the desired steam ressure in the digester. The heat in the llquid admitted to the digester will cause a portion of. the liquid to be converted into steam when the pressure on the liquid is reduced. By proceeding in this manner a suflicient steam pressure can be maintained in the digester until all the ulp is discharged whereupon the valve 5 is closed.

-As the waste liquor admitted from tank H is substantially identical with the cooking liquor in the, digester, save for some dilution which may occur from condensationof steam admitted through pipe I, the use of the flushing liquor does not interfere with, or

increase the difliculty of recovering the-valuable chemical constituents of the waste liquor. These constituents may be recovered by drawing oil the surplus liquor fromvreservoir F, evaporating. and burning the residue in the usual manner.

An important advantage of the apparatus described is had from the fact that the pressure, as well as the temperature-of the black liquor, is built up in tank H in a very sim le manner by the direct action of steam un er pressure. While a pump such as pump G working a ainst a head of only a few feet is quite satis a'ctory, itis very diflicult to pump the waste liquor, even, if cold, against the head necessary to cause it to enter the dithe direct pressure of steam to blow into the digester black liquor heated to a temperature corresponding to a steam pressure not less than the pressure in the digester.

2. The method offremoving pulp from a pulp digester, which consists in blowing black liquor into the digester by the direct action on the black liquor of steam of a pressure not less than the pressure in the digester,'whereby the black liquor introducedinto the digester is heated before introduction to a temperature at least as high. as the temperature m the di ester, and the black liquor does not lower te pressure in the digester. i CHARLES N. WAITE. v Witnesses:

ARNOLD KATZ, D. STEWART. 

